Elements and compounds

Group I: The Alkali metals

The elements in group 1 of the periodic table are called the alkali metals. The group 1 alkali metals are extremely reactive and need to be stored under oil. If they aren’t stored under oil, they may react with oxygen in the air and water.

Listed below are the names of all group 1 alkali metals:

  • Lithium
  • Sodium
  • Potassium
  • Rubidium
  • Caesium
  • Francium
Atom and symbol Electronic structure
Lithium ( Li) 2,1
Sodium (Na) 2,8,1
Potassium (K) 2,8,8,1


Ionic symbol Electronic structure
Li+ 2
Na+ 2,8
K+ 2,8,8


As seen in the table above, all alkali metals have a valency of 1 and they form ionic compounds when reacted with the group VII metals (The Halogens)


Physical properties of group 1 alkali metals
Group 1 alkali metals are very soft metals; they can be easily cut using a knife! Their softness increases down the group.
As they are extremely reactive metals, they get easily tarnished when exposed to air. This can be noticed by the formation of a silvery shiny flim on their surface.
Group 1 alkali metals are good conductors of heat and electricity.
They all have low melting points. Melting points for group 1 alkali metals decreases down the group.
Their densities are very low and tend to increase down the group.


Chemical properties of group 1 alkali metals
The group 1 alkali metals are extremely reactive and their reactivity increases down the group.

All alkali metals react violently with cold water to produce a metal hydroxide and hydrogen gas.

Here are some examples of the first 3 alkali metals and water:

Lithium + water à lithium hydroxide + Hydrogen gas

Sodium + water à Sodium hydroxide + Hydrogen gas

Potassium + water à Potassium hydroxide + Hydrogen gas


Group VII: The Halogens

The elements in group 7 of the periodic table are called the halogens.

The halogens in the periodic table have been listed below:

  • Fluorine
  • Chlorine
  • Bromine
  • Iodine
  • Astatine
Atom and symbol Electronic structure
Chlorine (Cl) 2,8,7
Bromine (Br) 2,8,18,7
Iodine (I) 2,8,18,18,7


Ionic symbol Electronic structure
Cl 2,8,8
Br 2,8,18,8
I 2,8,18,18,8


Molecular formula State at r.t.p Colour
Cl2 Gas Greenish yellow
Br2 Liquid Red-Brown
I2 Solid Black crystals (Sublimate to give purple vapour)



Physical properties of group VII elements (Halogens)
The colour of the halogens gets darker down the group
Melting and boiling points increase down the group
All halogens have diatomic molecules (which mean that each molecule is made up of 2 atoms!)
They show a gradual change from a gas (Cl2), through a liquid (Br2), to a solid (I2) as the density increases.
They form molecular compounds with other non-metallic elements, for example HCl.


Reactivity of Halogens
The reactivity in halogens increases up the group. Hence, the most reactive halogen is fluorine and the least reactive is astatine.


Displacement reaction in Halogens

Halogens experience a kind of reaction known as the displacement reaction. In this reaction, the halogen with the greatest reactivity displaces the halogen with lesser reactivity.

For example, if fluorine is made to react with potassium chloride, the chlorine (which is less reactive than fluorine) will get displaced and potassium chloride will change into potassium fluoride.


Group 0: The noble gasses

The noble gases belong to group 0 of the periodic table. They have a valency of 0, which means that their outer electron shell is complete. This means that they cannot share electrons and get involved in atomic bonding and thus are quite unreactive.

Uses of noble gases

Helium a. Used in party balloons (as the gas is quite less dense)

b. Liquid helium is used in low temperature research

c. Helium is mixed with oxygen and is used by deep sea divers.

Argon Argon is used to fill filament light bulbs
Neon a. Used in advertising lights

b. Used in lasers

Xenon Used in photographic flash lamps


Transition elements

The transition elements consist of many common elements that are used in day to day lives.

There are 3 series of transition elements in the periodic table.

Properties of transition elements

  • Transition elements are harder and stronger than the metals in Groups I and II.
  • They are less reactive and don’t react (corrode) so quickly with oxygen and/or water.
  • Transition elements have high melting points (except for mercury, which is a liquid at room temperature).
  • They form a range of brightly coloured compounds.
  • They are good conductors of heat and electricity.
  • Transition elements and their compounds both behave as catalysts. Hence, they’re used as catalysts in industrial manufacturing processes. For example, iron is used in the industrial production of ammonia gas.
  • They have more than one oxidation states.
  • They have higher densities.


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